Known in the art is a hinge joint for a screw planetary hydraulic drilling machine, comprising two universal joints interconnected by means of a shaft.
Each universal joint comprises a cylindrical casing whose inner wall is provided with a gear ring made therein. The casing houses two half-couplings which are arranged coaxially and engage the gear ring of the casing. The butt ends of the half-couplings, facing each other, have hemispheres made in the middle thereof to accomodate a ball, the radius of the latter being smaller than that of the hemispheres by a value proportional to the angle of turning of the hemispheres relative to the joint casing.
The casing is closed from the opposite sides with covers placed therein by means of a screw joint. The space between the gear rings of the half-couplings and the casing is filled with lubricant and is insulated with seals placed in the casing between the covers and the butt ends of the casing gear ring. Each of the seals is made as a rubber ring tightly fitted with its outer cylindrical face into the joint casing and with its inner face onto a half-coupling. Disposed at both sides of the ring on its flat end faces are rigid (metallic) rings of which one rests upon the gear ring of the casing and the other one contacts the inner butt end of the cover. In order to provide for skewness of the half-coupling relative to the joint casing, required in the course of operation, the rings have some gap provided between their inner diameter and the diameter of the half-couplings (see, for example, USSR Inventor's Certificate No. 543,730; Cl.E21B 3/12).
Displacement of the contacting faces of the rubber ring and the half-coupling, taking place under the action of the alternating contact load caused by pressing (oscillating) movement, results in additional one-sided deformation of the rubber rings. As a result of the non-uniform deformation of the rubber rings, the flushing fluid penetrates the gap formed between the rings and the half-coupling and, on getting into the joint space, washes out the lubricant.
Besides, high temperatures created during the well drilling cause, in the hinge joint employed in the drilling motor used for drilling oil and gas wells volumetric expansion of the lubricant which is squeezed out of the joint inner space. As a result, the gaps thus formed in the joint are filled up with the flushing fluid when the motor is lifted and the temperature drops.
A decreased amount of the lubricant and presence of the flushing fluid in the space of the universal joint result in a quick wearing of the gears of the rings of the half-couplings and the gears of the rings of the casing during transmission of the torque.